Professional educators demand that their methods and instructional resources be soundly based on research and theory. From its origins nearly 40 years ago, the PLATO[R] system has built the largest base of basic research on computer-based learning in the field. Beginning with research funded by the National Science Foundation and conducted at the University of Illinois and collaborating institutions, nearly 900 references on the PLATO[R] system are listed in the ERIC educational research database. This paper summarizes the research base of PLATO[R] Learning's instructional software, and describes the theoretical grounding of the curricula in the theory of reading, mathematics, and instructional design. It describes the PLATO[R] independent evaluation program and summarizes effectiveness studies performed as part of the ongoing program. PLATO[R]'s instructional design standards are described with nine tables, covering the areas of general design; standards for content/information; comparison of direct instructional models; standards for tutorials; standards for application practice; standards for problem solving activities and simulations; standards for information software; standards for tool software; and standards for tests. (Contains 77 references.) (AEF)